Belt tracking system



March 17, 1970 JONES ETAL BELT TRACKING SYSTEM 6 Sheets-Sheet 1 OriginalFiled May 24, 1968 INVENTORS HUGH L. JONES DAVID R. STOKES BYwd ATTORNEYS March '17, 1970 H. JONES ETAL 3,500,694

BELT TRACKING SYSTEM Original Filed May 24, 1968 6 Sheets-Sheet 2 INVENTR HUGH L. JON 5 BY DAVID R. STOKES ATTORNEYS March 17, 1970 I JONES ETAL3,500,694

BELT TRACKING SYSTEM Original Filed May 24, 1968 6 Sheets-Sheet 5INVENTORS HUGH L. JONES DAVID R. STOKES A T TORNE VS March 17, 1970 H.L. JONES ETAL BELT TRACKING SYSTEM 6 Sheets-Sheet 4 Original Filed May24, 1968 S m mE N T O R N T 0 W S T HUGH DAVID R. BY

March 17, 1970 JONES ET AL 3,500,694

BELT TRACKING SYSTEM Original Filed May 24, 1968 6 Sheets-Sheet 5OOOOOOO OOOOOOO L7 INVENTORS 52% a s Tms F IG. 6

A T TORNEYS March 17, 1970 H. JONES ET AL BELT TRACKING SYSTEM 6Sheets-Sheet 6 Qriginal Filed May 24, 1968 FIG. 7

United States Patent 3,500,694 BELT TRACKING SYSTEM Hugh L. Jones andDavid R. Stokes, Rochester, N.Y., assignors to Xerox Corporation,Rochester, N.Y., a corporation of New York Continuation of applicationSer. No. 731,755, May 24,

1968. This application Mar. 27, 1969, Ser. No. 826,740

Int. Cl. F16h 7/18 US. Cl. 74241 6 Claims ABSTRACT OF THE DISCLOSURE Abelt tracking arrangement for use with a belt supporting roller whereinthe shaft for the roller is mounted for short pivotal movement about anaxis normal to its axis and which lies in a plane that bisects the angleof the belt runs on either side of the roller.

This is a continuation of application Ser. No. 731,755, filed May 24,1968, now abandoned.

This invention relates to belt transport apparatus and particularly, toimprovements in a belt tracking system for a photoconductor plate in theform of an endless belt. The tracking system arranged in accordance withthe present invention is particularly adapted for use with seleniumbelts in automatic copiers/reproducers that are constructed for highspeed operation and capable of having their sequence timing variedthereby per' mitting variable speeds of output.

As is well known in recent years, the steadily increasing size ofvarious industries has required an enormous increase in the amount ofpaper work that must be accomplished, maintained and made available forwide interplant circulation. In the present day commercial automaticcopiers/reproduction machines, which are adapted to produce copies ofbetween and 60 8 x 11" sheets of copy per minute, the photoreceptordevice is in the form of a drum which rotates in timed unison relativeto a plurality of processing stations.

The limiting feature in these present day machines is the use of thexerographic drum which seriously limits the positioning and action ofeach of the processing devices and, in particular, the requirement ofpresenting a flowing image upon the Xerographic drum as a document isbeing scanned.

The mechanism which accomplishes the scan of a fixed document in thedrum type copier/duplicator generally involves a slidable carriage forsupporting illumination lamps in addition to drive mechanisms, levers,pulleys, switches, etc. for accomplishing scanning of the document. Asthe demands for faster copying or duplicating has come about, theseconventional machines generally have been modified in their respectivedrive systems and electrical circuits in order to accomplish a fasterscan for the scanning mechanisms already in the machine. The result ofthese modifications is to propel the structures that go to make up thescanning mechanisms at very great speeds and, as will be apparent, willplace great undue burdens upon the structural supports of the machineand the scanning mechanism.

As a solution for overcoming the multitude of disadvantages for highspeed copying, the latest machine concept for copiers utilizes flashexposure of a document and the arrangement of a moving photoconductormaterial in the form of a belt held in a flat condition at the instantof exposure. However, the use of photoconductor belts require extremecare since these belts are very delicate, are easily damaged and themovement thereof through processing stations in a reproduction 3,500,694Patented Mar. 17, 1970 ICC machine must be accomplished with highprecision and with as little irregular movement as possible.

It is therefore the principal object of this invention to improvecopiers/reproduction machines of the type having a belt form ofphotoreceptor by maintaining belt travel in accurate alignment with apredetermined path of movement.

Another object of this invention is to improve the ability of belthandling apparatus for controlling precise movement of the belt duringcontinuous movement thereof.

Another object of this invention is to improve belt tracking mechanismsfor an endless belt by producing corrective tracking which will produceminimum strain upon the belt.

These and other objects of this invention are obtained by means of abelt tracking arrangement applied to one of the rollers in an endlessbelt conveying system wherein the roller has its entry and exit runs atan angle less than The roller is mounted for rocking movement on an axiswithin the plane of the bisector of the angle formed by the two runs.The roller shaft is mounted at its ends on support arms which areadapted to pivot in unison, in opposite directions and on an axis whichis in the bisector plane and is parallel to the roller shaft.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the following detaileddescription of the invention to be read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an exploded right-hand perspective view of a reproductionmachine incorporating the present inven tion therein with the processingcomponents separated to better illustrate the invention;

FIG. 2 is a schematic sectional view of the reproduction machine showingthe various xerographic processing stations;

FIG. 3 is a perspective view of the photo-conductive belt assemblyutilized in the machine;

FIG. 4 is an elevational view of the belt assembly as seen from the rearof the machine;

FIG. 5 is an elevational view of the other side of the belt assembly asseen from the front of the machine;

FIG. 6 is an elevational view of the belt assembly with the belt mountedthereon partly in section to show various internal parts;

FIG. 7 is a sectional view taken along the line 77 in FIG. 6; and,

FIG. 8 is a partial view of the lower section as seen from the front ofthe developer assembly showing the selenium belt in a relaxed condition.

For a general understanding of the illustrated copier/repreductionmachine, in which the invention may be incorporated, reference is had toFIGS. 1 and 2 in which the various system components for the machine areschematically illustrated. As in all electrostatic systems such asxerographic machine of the type illustrated, a light image of a documentto be reproduced is projected onto the sensitized surface of axerographic plate to form an electrostatic latent image thereon.Thereafter, the latent image is developed with an oppositely chargeddeveloping material to form a Xerographic powder image, cor respondingto the latent image on the plate surface. The powder image is thenelectrostatically transferred to a support surface to which it may befused by a fusing de vice whereby the powder image is caused permanentlyto adhere to the support surface.

In the illustrated machine, an original to be copied is placed upon atransparent support platen P fixedly arranged in an illuminationassembly generally indicated by the reference numeral 10, arranged atthe left end of the machine. While upon the platen, an illuminationsystem, to be described herein, flashes light rays upon the originalthereby producing image rays corresponding to the informational areas onthe original. The image rays are projected by means of an optical systemfor exposing the photosensitive surface of a Xerographic plate in theform of a flexible photoconductive belt arranged on a belt assemblygenerally indicated by the reference numeral 11.

The photoconductive belt assembly 11 is slidably mounted upon a supportbracket secured to the frame of the machine and is adapted to drive aselenium belt 12 in the direction of the arrow as shown in FIG. 2 at aconstant rate. During this movement of the belt, the reflected lightimage of an original on the platen is flashed upon the xerographicsurface of the belt, at such a speed measured in microseconds, that therelative motion of the light rays comprising the light image and thebelt surface is minimal. The belt surface that intercepts the light rayscomprises a layer of photoconductive material such as selenium on aconductive backing that is sensitized prior to expose by means of acharging corona generator device indicated at 13.

The flash exposure of the belt surface to the light image discharges thephotoconductive layer in the areas struck by light, whereby thereremains on the belt a latent electrostatic image in image configurationcorresponding to the light image projected from the original on thesupporting platen. As the belt surface continues its movement, theelectrostatic image passes through a developing station B in which thereis positioned a developer assembly generally indicated by the referencenumeral 14 and where the belt is maintained in a flat condition. Thedeveloper assembly 14 comprises a vertical conveying mechanism whichcarries developing material to the upper part of the belt assembly 11whereat the material is dispensed and directed to cascade down over theupwardly moving inclined selenium belt 12 in order to providedevelopment of the electrostatic image.

As the developing material is cascaded over the xerographic plate, tonerparticles in the development material are deposited on the belt surfaceto form powder images. As toner powder images are formed, additionaltoner particles are supplied to the developing material in proportion tothe amount of toner deposited on the belt during xerographic processing.For this purpose, a toner dispenser generally indicated by referencenumeral 15 is used to accurately meter toner to the developer materialin the developer assembly 14.

The developed electrostatic image is transported by the belt to atransfer station C whereat a sheet of copy paper is moved at a speed insynchronism with the moving belt in order to accomplish transfer of thedeveloped image. There is provided at this station a sheet transportmechanism generally indicated at 16 adapted to transport sheets of paperfrom a paper handling mechanism generally indicated by the referencenumeral 18 to the developed image on the belt at the station B.

After the sheet is stripped from the belt 12, it is conveyed into afuser assembly generally indicated by the reference numeral 21 whereinthe developed and transferred xerographic powder image on the sheetmaterial is permanently afiixed thereto. After fusing, the finished copyis discharged from the apparatus at a suitable point for collectionexternally of the apparatus.

Suitable drive means may be arranged to drive the selenium belt 12 inconjunction with timed flash exposure of an original to be copied, toeffect conveying and cascade of toner material, to separate and feedsheets of paper and to transport the same across the transfer station Cand to convey the sheet of paper through the fuser assembly in timedsequence to produce copies of the original.

It is believed that the foregoing description is sufiicient for thepurposes of this application to show the general operation of anelectrostatic copier using an illumination system constructed inaccordance with the invention.

The selenium belt comprises a photoconductive layer of selenium which isthe light receiving surface and imaging medium for the apparatus, on aconductive backing. The belt is journaled for continuous movement uponthree rollers 45, 46 and 47 located with parallel axes at approximatelythe apex of a triangle. During exposure of the belt 12, the portionthereof being exposed is that part of the belt run between the upperroller and the lower roller 46. As shown in FIG. 3, the photoconductivebelt assembly 11 is illustrated with the selenium belt removed in orderto illustrate the assembly mechanisms located adjacent the belt.

The upper and lower pulleys 45 and 47 are journaled in two side plates48 and 49, each having the general configuration of a triangle. Theupper apex of the side plate 48 is formed with an opening for containingand supporting a bearing 50 which rotatably supports one end of theshaft 51 for the roller 45. At the other end, the shaft 51 is journaledin a bearing 52 supported at the upper apex for the side plate 49 in thesame manner; however, the shaft extends beyond the side plate andthrough an opening 53 formed concentrically with the shaft in a mainsupport plate 54 for the reproduction apparatus. A shaft extension 55 isformed on this end of the shaft and extends through the opening 53.

The purpose for the extension 55 of the shaft 51 is to support a drivemechanism for rotating the roller 45 when the belt assembly 11 is inoperating position, that is, when the side plate 49 is positionedagainst the main frame plate 54, and still permit the easy removal ofthe belt assembly 11 from the machine frame. To this end the main frameplate 54 is provided with a quick disconnect mechanism for releasablyreceiving the extension 55 and to become drivingly engaged with theextension when the assembly 11 is in operating position. As shown inFIG. 6, the opening 53 in the frame plate 54 is covered on one side, theside removed from the roller 45, by a support ring 56 suitably securedby bolts to the remote side of the plate 54. The ring 56 is formed withan opening 57 concentric with the opening 53 and the shaft 51 when inoperating position. Within the opening 57 is retained a bearing 58having an inner race 60 secured by a lock ring 61 to a drive member 62rotatably retained by the bearing 58 upon the plate 54. The drive member62 is formed with a concentrically positioned recess 63 into which isinserted the extreme end of the extension 55. This end of the extensionhas a snug fit within the opening 63 and serves to precisely locate theaxis of the shaft 51 relative to the support frame plate 54 therebyinsuring accurate driving of the selenium belt 12.

The driving connection between the shaft 51 and the drive member 62 isin the form of a one way clutch 64 drivingly connected between theextension 55 and the member 62. The clutch 64 is adapted to becomeengaged when the assembly 11 is in operating position in order to permitrotation of the roller 45 by rotation of the drive member 62. When thebelt assembly 11 is slightly removed or pulled away from the frame plate54, the clutch 64 and the extension 55 are pulled out of the recess 63in the drive member 62 in order to disengage the connectiontherebetween.

The outer extremity of the drive member 62 is adapted to support a drivegear 65 which meshes with a smaller gear 66 secured to a pulley 67drivingly connected by way of a timing belt 68 to a drive system to bedescribed hereinafter.

The side plates 48 and 49 are maintained in parallel planes and rigidlysupported in spaced relation for supporting the rollers 45, 46 and 47and all of the other structures that comprise the belt assembly 11 by aninternal T-member to be described below. The side plates 48, 49 alsosupport a flat front plate 69 and a rear flat plate 70 by suitable meanssuch as screws 71. Each of the plates 69 and 70 are formed with aplurality of apertures 72 which extend through the respective plates. Aswill be described in detail hereinafter, the plates 69 and 70 serve asvacuum holddown plates for supporting the selenium belt 12 flat againstthe plates during movement thereof on the assembly 11. The apertures 72are in communication with a plenum chamber which, in turn, is connectedby suitable ducts to a vacuum chamber for drawing air inwardly throughthe apertures 72 and thereby hold by vacuum the adjacent runs of thebelt 12.

The lower roller 47 is similarly mounted upon the side plates 48, 49 asis the left-hand end of the shaft 51 for the roller 45. The shaft 73 forthe roller 47 may be suitably supported in ball bearings similar tobearing 50 supported in the side plates 48, 49.

As previously stated, the selenium belt assembly 11 is slida-blysupported on the machine frame plate 54. To this end, the frame plate 54has extending horizontally and perpendicular thereto a support arm 75having a crosssection shaped as the letter T.

Secured to the upper cross bar of the support arm 75 is the lower race76 of a slide suspension arm which also includes an upper race 77secured to the upper leg of a. T shaped channel member 78 securedbetween and supporting the side plates 48, 49 of the belt assembly 11.The channel member 78 is approximately positioned within the centerspace of the belt assembly and also has secured on one side thereof arace 80 of another slide suspension arm which has its other race 81secured to the adjacent lower section of the support arm 75. Uponviewing FIGURE 7 it will be apparent that a belt assembly 11 is adaptedto be moved toward and away from the frame plate 54 and to be supportedthereon for sliding movement by the support arm 75, the slidingcharacteristic being supplied by the slide suspension arms comprisingthe races 76, 77 and 80, 81. When mounted on the arm 75 in cantileverfashion, all of the mounting means for the belt assembly are positionedwithin the confines of the assembly as defined by the axes of therollers 45, 46, 47. This arrangement allows access to and clearance forthe belt permitting removal or installation of the same withoutendangering its structure.

The T-members 75, 78 together with the slide suspension arms connectedtherebetween and the shaft extension 55 and the drive member 62, allowthe belt assembly 11 to be removed and positioned for support upon thefixed support plate 54 without disrupting or requiring a driveconnection and, to insure safe positioning of the belt and the assembly.Guide slots 79 formed in the plate 54 receive locating pins secured tothe plate 49 for precisely locating the assembly 11 once it has beenmoved into operating position.

Each of the side plates 48, 49 is formed with axially aligned openings82 in order to accommodate the support arm 75 during mounting or removalof the assembly 11. These openings, only one of which is shown, alsoserve to permit the extension therethrough of a locking mechanism forreleasably holding the assembly 11 upon the plate 54 when the assemblyhas been moved thereto.

This locking mechanism includes a pair of blocks 83, 84 secured withinthe chamber defined by the plates 48, 49 and one to each of theseplates. A shaft 85 is slideably received in the blocks 83, 84 andextends through the opening 82 formed in the plate 48 a short distanceto accommodate a handle 86 at that end thereof. The other end of theshaft 85 extends through the other opening 82 formed in the side plate49 and extends beyond an opening formed in the frame plate 54 in linewith the opening 82. This end of the shaft 85 terminates in a bentportion 87 (see FIG. 4) which is adapted to be moved to assume differentradial directions upon rotation of the shaft 85 by the handle 86. Thebent portion 87 is adapted to be received in a depression 88 formed in acircular lock member 89 secured upon the outer surface of the frameplate 54.

Normally, the shaft is urged outwardly or to the right as viewed in FIG.6 by a spring 90 held in compression between the handle 86 and one sideof the block 83. When the assembly 11 is removed from the frame plate54, the spring 90 will cause the bent portion 87 to abut against theblock 84.

In order to lock the assembly 11 against the plate 54 and assuming thatthe assembly 11 is properly oriented upon the plate, the handle ispushed toward the adjacent side plate 48 in order to drive the bentportion 87 through the opening 82 in the plate 49 and the adjacentopening in the frame plate 54. Rotation of the handle while so depressedwill rotate the bent portion 87 in position to be in alignment with thedepression 88 formed in the lock member 89. Upon release of the handle86, the spring 90 Will force the shaft 85 outwardly thereby causing thebent portion 87 to assume a locked position within the sides of thedepression 88. In this manner, the assembly 11 remains rigidly locked inproper position and alignment upon the frame plate 54.

As previously stated, the apertures 72 formed in the vacuum plates 69and 70 are in communication with plenum chambers which, in turn, areconnected to a vacuum manifold which is suitably connected to anevacuation system, such as a blower and the like, in order to produce aslight vacuum within the plenum chambers. As shown in FIG. 7, the frontor exposure side of the belt assembly 11 is connected by means of endstrips 92 to a rear base 93 mounted parallel to but spaced slightly fromthe front vacuum plate 69. The flat chamber formed between the plates 69and 93 and the end strips 92 define a vacuum plenum having an outletslot 94 (see FIG. 4) which is arranged, when the assembly 11 is inlocked position upon the plate 54, to be in communication with anopening formed in the plate 54. The edges of the slot 94 are gasketed sothat when in abutment with the adjacent surface of the frame plate 54and in alignment with a slot opening formed therein of a size and shapeas the opening 94, there will be a minimal amount of leakage of airthrough these abutting surfaces.

The opening 94 may be suitably connected to a hose or manifold to asuitable blower which would in operation evacuate air from the plenumchamber and cause the flow of air inwardly through the openings 72. Thisvacuum condition will cause the selenium belt 12 to be drawn against theplate 69 during movement of the belt during processing by the machine.Since the plate 69 lies in alignment with the exposure station for theselenium belt, it is imperative that the selenium belt, as it movesacross the station, be as flat as possible so that light rays impingingupon the selenium belt at this area area will be in focus at all points.

Similarly, the rear vacuum plate 70 combines with a parallel spaced baseplate 96 and end strips 97 to form a second plenum chamber which is alsoconnected to a suitable opening in the base plate 54 and connected to ablower or vacuum producing apparatus. The rear vacuum plate 70 and itsrelated plenum structure is adapted to hold the selenium belt in a fiatplane on this side of the belt assembly, which side is adjacent, as willbe described hereinafter, to a development apparatus which requires thatthe selenium belt be or remain in a flat condition.

As previously stated, the selenium belt rollers 45 and 47 are mountedfor rotation upon the side plates 48, 49, being held against any othermovement relative to the side plates by suitable mounting bearings. Inorder to permit the mounting and dismounting of a selenium belt 12 uponthe belt assembly 11, the assembly is provided with an arrangement formoving the third roller 46 inwardly in order to form a slack in the belt12 for permitting its removal by sliding axially of the rollers. As partof this arrangement, the roller 46 is rigidly secured upon a shaft 100,the ends of which are each mounted within a selfaligning bearing element101 adapted to be secured to each support arm 102, 103.

Each of the support arms 102, 103 is arranged for longitudinal movementfor one operative function therefor and, for limited rocking or slightpivotal movement for another operative function. To this end, each ofthe support arms comprises a first slide member 104 to which the bearingelement 101 is secured for Supporting the roller 46 upon the beltassembly and a second slide member 105 slidably mounted relative to thefirst member. In order to accomplish sliding movement of one slidemember relative to the other, the member 104 is formed with an elongateddepression 106 running along the longitudinal axis thereof and, withinthe depression, the slide member 105 conforms and is held againstremoval therefrom by suitable lock strips 107 mounted in parallel to theadjacent edges of the member 104 in overlapping relationship relative toadjacent edges of the member 105. When mounted together, the membersresemble a slide rule device which may be elongated by extending themembers.

The support arms 102, 103 are supported by pivot pins 108, each securingto one of the arms to the lower portion of the side plates 48, 49. Eachpin 108 is rotatably fastened to the slide member 105 and is slidablyrelated to the first member 104. This arrangement has the effect ofpreventing axial movement of the second slide member 105 while allowingsliding movement of the first member 104 relative to the second member.

Manually operated control means are provided for producing simultaneoussliding movement of each first member relative to the respective secondmember in order to move the roller 46 inwardly relative to the beltassembly to permit the removal or installation of the selenium belt 12.The end of the first member 104 remote from the end thereof whichsupports the roller shaft 100 is provided with a cam follower 109. Asshown in FIG. 8, the follower extends in a direction normal to thelongitudinal axis of the support arm 102 and has a lateral extending camsurface 110 adapted to cooperate with a cam 111 formed as asemi-circular disc and being mounted eccentrically relative to thesemi-circular cam surface 112 thereon. Each of the cams 111 is securedfor rotation upon a shaft 113 which in turn, is mounted for rotation onthe side plate 48, 49 of the belt assembly. In being secured to theshaft 113, the cam surface 112 for each of the cam plates 111 will bemoved in unison when the shaft is rotated and, upon rotation, willsimultaneously engage the camming surface 110 of each of the camfollowers 109.

Rotation is imparted to the shaft 113 by way of a manually actuablehandle 114 secured to one end of the shaft extending through the sideplate 48. As shown in full lines in FIG. 5, the handle 114 is positionedsuch that the cam, plates 110 as shown in FIG. 7, is against theshortest camming position for the cam surfaces 110 in fact, there is aslight spacing between the surface 110 and the follower 109, therebyallowing the slide member 104 to be extended outwardly to its maximum,belt supporting and tensioning limit. When the handle 114 is moved tothe dotted position in FIG. 5, which corresponds to its full lineposition in FIG. 8, the cam plates 111, being moved thereby, willcontact the surface 110 at its high points and drive the support member104 along its longitudinal axis to the position of the cam follower 109shown in full lines in FIG. 8. With each slide members 104 being therebymoved, the roller 46 is moved inwardly to the position shown in FIG. 8.In this position of the roller, an operator may remove the selenium belt12, which will be in a loose condition from the selenium belt assembly11.

Normally the support slide member 104 is held in its outermost maximumbelt tensioning limit by means of a pair of relatively stiff springs 115each having one end secured to a post 116 secured to the member 104 atearn follower 109 and their other ends secured to a post 117 secured tothe support member 105. The post 117 extends through a slot 118 formedin the support member 104 being arranged to permit extension of the post117 therethrough and movement of support member 104 relative to the post117. Normally the springs 115 are held extended between the post 116,117 thereby normally maintaining the slide members 104, 105 toward theirextended position.

This arrangement places a spring bias upon the sup porting shaft for theroller 46 toward its fully extended position during operation of thebelt assembly. The springs 115, therefore, also serve to placeappreciable tension upon the selinium belt 12 during movement thereof onthe belt assembly. In the event that the photoconductive belt is to beremoved and replaced by another belt, the operator manipulates thehandle 114 from the position shown in dotted lines to the position shownin full lines in FIG. 8 thereby actuating the support member 104inwardly against the bias provided by the springs 115. This movement isaccomplished rather smoothly with the shaft 100 being moved from itsoutermost operative position to its most inwardmost position that isparallel to the operative position.

Each of the support arms 102, 103 is adapted to be rotated about itsrespective pivot pin 108 and in opposite directions in order to rock theshaft 100 in a plane normal to the plane defined by axes of the supportarms. This rocking movement is provided in order to permit tracking ofthe selenium belt during its continuous movement around its threesupport rollers. This tracking capability is provided in order tomaintain the belt in a precise predetermined position for allxerographic stations surrounding the belt assembly 11 when in operation.The tracking is accomplished by mechanisms which are adapted to slightlypivot each of the arms 102, 103 in opposite direction about theirrespective pivot pins 108, as previously stated.

As shown in FIG. 7, the end of each slide member remote from the endadjacent the shaft 100 is formed as a yoke element 120 that is inalignment with the longitudinal axis of the slide member. This end ofeach support arm is also formed with a slot 121 having its longitudinalaxis normal to the longitudinal axis of the member 105. Each slot isadapted to accommodate a screw 122 having its threaded portion securedinto the inner surface of the plates 48, 49 of the belt assembly 11.Portions of the screws 109 that are cooperable with the sides of theslots 121 are free of threads and serve to maintain the arms 102, 103against the side plates for the selenium belt assembly. The inner edgesof the yoke element 120 are formed with camming surfaces 123 and 124held in abutment against a cam shaft 128 which extends through the beltassembly 11 and is mounted in suitable bearings 130 secured to the sideplates 48, 49.

As shown in FIGS. 6 and 7, the shaft 128 has its on-axis end portions131 mounted in the bearings 130 and portions 132 eccentric relative tothe main portion of the shaft. Each eccentric portion 132 is adapted toengage one or the other of the camming surfaces 123, 124. Upon rotationof the shaft 128 in either direction, each eccentric portion is adaptedto drive the corresponding yoke member 120 laterally in oppositedirections in order to pivot the corresponding support arms 102, 103about their respective pivots in opposite rotational directions therebyeffecting opposite movements to each end of the shaft 100.

In order to provide movement of both ends of the shaft 100 in oppositedirections thereby effecting a greater available movement to the roller46, the eccentricity of the cam portions 132 are in opposite directions.Upon rotation of the shaft 128, the axis of the main portion thereofwill remain fixed and will move the cam 132 in the same direction toeffect corresponding pressures upon one of the camming surfaces 123, 124in opposite directions, that is, the camming surface 123 for one of thesupport arms 102, 103 will be moved in one direction, and the carnmingsurface 124 of the other arm will be moved in the opposite direction.The effect of this opposite directional movement of the support arms102, 103 will produce rocking movement of the shaft 100, andconsequently the roller 46. The spherical bearings upon which the shaft100 is mounted will permit this slight relative rocking movement of eachend of the shaft relative to its fixed mounting arrangement in the formof the members 104.

As shown in FIG. 5, the axes of the shaft 100, the pins 108 and theshaft 128 for the support arm 102 are in alignment and, for both arms.102, 103 these axes lie in a common plane. This plane is in coincidencewith the bisector of the angle formed between the planes of the beltruns on either side of the roller or, in other words between the planedefined by the axes of the shafts 100 and 73 and the plane defined bythe axes of the shaft 100 and the shaft 51. With the support arms 102,103 being equally pivotable in either direction, the roller 46 duringtracking operation, will rock about an axis lying on the bisector planeand positioned intermediate the ends of the roller. For tracking then,such skew action of the roller will effect an angular relationship ofthe roller relative to the direction movement of the belt therebycausing the same to steer or follow the roller surface and be displacedlaterally in order to return the belt back to a centered position ratherthan exerting pressure on the belt adjacent one edge portion thereof. Inthis manner, pressure is applied equally to all portions of the beltaffected during tracking action thereby minimizing the tendency of thetracking arrangement to adversely affect belt structure by exertingundue pressures of the belt structure adjacent one edge or the portionbetween the midline of the belt and one edge. With the axis of pivotingof the roller 46 lying on the bisecting plane for the planes of theselenium belt runs, the deflection of the ends of the roller occurs inopposite direction to provide maximum belt correction with minimumroller skewing. Preferably the roller 46 is covered with a rubbercoating which will prevent slippage of the belt as it steers duringtracking. During rocking of the shaft 100, both edges of the belt areaffected equally and, as the skewing increases during tracking action,any tendency of the belt to lessen in circumference will cause movementof the roller 46 inwardly against the tension of the springs 115 whichserve as shock absorbers for tracking action.

In the event that the selenium belt 12 is removed and a new one appliedto the belt assembly which has a slightly larger or smallercircumference, the springs 115 will always maintain the same pressure ofthe roller 46 upon the belt thereby insuring the same tension upon abelt regardless of its circumferential size. The arrangement alsoeliminates any two directional forces being applied to the belt whichcould have a destructive effect upon the relatively thin film of thephotoconductive material on the belt. In addition, with the axis of theroller 46, lying on the bisecting plane of the angle between theadjacent belt runs during rocking movement of the roller 46, there is aminimum of deflection, caused by skewing of the belt, along the exposurebelt run between the rollers 45, 46 thereby minimizing the effect ofbelt skewing upon the imaging abilities on this run during an exposureof an original.

Drive means are provided in the belt assembly 11 in order to impartcontrolled instantaneous rotation of the shaft 128 in either directiondepending upon the slipping of the belt axially relative to the shaftsof the rollers 45, 46, 47 in either direction. The shaft 128 has its endportion 131 extending through the side plate 49 and terminating in agear 133 secured thereto. The gear 133 is in mesh with a second gear 134secured to a shaft 135 for a reversible motor M-ll and gear reductionarrangement 136. Energization of the motor M-11 will impart rotation tothe gears 133, 134 for rotating the shaft 128 in either directiondepending which direction the belt 12 slips relative to supportingrollers.

Energization of the motor is accomplished by means of a sensing devicecomprising a potentiometer POT (not shown) having a sensing fingerpositioned adjacent an edge of the belt 12. In the event the beltstrays, the potentiometer and its associated circuitry will produce asignal to cause energization of the motor M-11 and rotation thereof in adirection to cause the roller 46 to rock into a position to force thebelt back toward the direction opposite the slipping direction.

What is claimed is:

1. A belt tracking apparatus for use with a belt assemly having aplurality of rollers with supporting shafts for guiding and supportingan endless belt for movement therearound and with the axes of the shaftssubstantially in parallel comprising a support arm pivotally connectedto each end of the shaft of one of the rollers,

means for pivotally mounting said support arms on a common axissubstantially parallel to the axis of said shaft, said shaft and saidpivotal axis defining a plane arranged to bisect the angle between theplanes of the belt runs on either side of said roller and control meansfor pivotally actuating said support arms in opposite directions inresponse to deviation of the belt from a pre-arranged belt path wherebysaid roller is pivoted about an axis in said bisector plane and normalto the axis of said shaft.

2. The apparatus of claim 1 wherein each support arm comprises a firstslide member connected to the corresponding end of said shaft and asecond slide member pivotally mounted on said common axis and slidablysupporting said first member.

3. The apparatus of claim 1 including means operatively connected tosaid support arms and said roller shaft for normally exerting a force onthe roller tending to enlarge the belt thereby producing tension on thebelt.

4. The apparatus of claim 1 wherein said control means includes a drivemeans connected to each control arm and arranged to produce equal andopposite pivotal movement upon said control arms.

5. A belt tracking apparatus for use with a belt assembly having aplurality of rollers with supporting shafts for guiding and supportingan endless belt for movement ,therearound and with the axes of theshafts substantially in parallel comprising a support mechanism havingan arm rotatably supporting each end of the shaft of one of the rollers,

means for pivotally mounting said support mechanism about an axissubstantially normal to the axis of said shaft, said shaft and saidpivotal axis defining a plane approximately bisecting the angle betweenthe planes of the belt runs on either side of said roller,

and control means connected to said support mechanism and adapted toproduce movement of said arms in opposite directions in response todeviation of the belt from a prearranged belt path whereby said rolleris pivoted about an axis in said bisector plane and normal to the axisof said shaft.

6. The apparatus of claim 5 wherein each arm is mounted for pivotalmovement on a common axis and, wherein the movement of said arms inopposite directions is a pivotal movement along said common axis.

References Cited UNITED STATES PATENTS 2,988,141 6/1961 Madden et al.74-241 XR 3,156,129 11/1964 Greiner 7424l JAMES A. WONG, PrimaryExaminer

